This invention relates to uncured furazan oxide modified rubbers, to improved methods of processing said rubbers to rubber compositions containing said rubbers, and to methods for reducing the rolling resistance of tires. More particularly, the present invention relates to a process for improving the properties and reducing the undesirable odor of rubber compositions containing aromatic furazan oxides, and to filled vulcanizates made by vulcanizing mixtures of said rubber compositions and reinforcing fillers.
It is known that rubber compositions generally are combined or "compounded" with various other materials before being cured and/or put into use. Some of these added materials improve the properties of the end product in service while others improve processing properties of the uncured compositions. In some instances, both effects may be achieved. It is also known that the various chemicals, pigments and other materials so used, both organic and inorganic, can interact in various ways to produce desirable or deleterious effects. For further discussions of rubber processing and materials used therein, see, for example, Encyclopedia of Polymer Science and Technology, published by John Wiley and Sons, New York (1970), particularly Vol. 12, page 280 and The Vanderbilt Rubber Handbook, R.T. Vanderbilt Company, Norwalk, Conn., 06855 (1968), particularly Sections 6, 7, 8, 9 and 11.
Vulcanizing agents, plasticizers, extenders, fillers, pigments, etc. generally are incorporated into vulcanizable rubber compositions so that the rubber can be cured or vulcanized in a mold to form useful articles. It often is necessary to include processing aids in rubber compound prior to molding and curing. These processing aids are primarily intended to improve the mixing of the ingredients of the rubber compound, the processability of the rubber during processing, the mold or mill release properties of the rubber, tack and green strength without seriously adversely affecting the properties of the cured rubber.
Carbon blacks are used in rubber formulations and vary widely as to their characteristics and effects on rubber formulations. In rubber formulations, carbon black is used as a reinforcing filler. Many carbon blacks of the channel and furnace types with varying characteristics have been utilized because they impart varying desirable characteristics to the rubber.
Benzofurazan oxides, and their analogs and isomers are known compounds, and many descriptions of them and procedures for their preparation have appeared. See, for example, Kaufman et al, "Chemical Reviews", Vol. 59, page 429 and following (1959) and Mallory et al, Organic Synthesis collective Vol. IV, pp. 74 and 75, John Wiley and Sons, New York (1963). The following U.S. patents also describe procedures for preparing furazan oxides of various types: U.S. Pat. No. 4,185,018 to Fah; U.S. Pat. No. 3,528,098 to Shaw; and U.S. Pat. No. 2,424,199 to Ter Horst. In considering previous descriptions of furazan oxides and related compounds, it should be noted that nomenclature used for these compounds has not been consistent, in part due to uncertainty as to their structures and predominant isomeric form. For example, they have been described as furazan oxides, as ortho dinitroso benzenes or di(nitrile oxides), isobenzofuroxans, benzofuroxans, benzofurazan-N-oxides and benzofurazan oxides. It is believed that the latter term is the modern and preferred nomenclature, and it shall be used in this specification and the appended claims.
Studies of furazan oxides and related compounds in rubber have been reported. For example, Rehner and Flory have indicated in Industrial and Engineering Chemistry, Vol 38, page 500 et sec, that ortho dinitroso benzene is inactive in butyl rubber as a vulcanizing agent. In contrast, the para isomer is said to be very active. U.S. Pat. No. 3,931,121 to Davis et al, describes the curing of elastomeric polymers with poly(chloronitroso) compounds. U.S. Pat. No. 3,931,106 to Crosby et al, describes the use of dinitrile oxides, (generated in situ from furazans), in rubber cross-linking.
British Patent No. 1,586,861 describes the use of organic compounds which are sources of adjacent nitroso groups on a six-membered aromatic ring for modifying polymeric materials containing carbon-carbon unsaturation. Examples of such polymeric materials include polybutadiene, styrene-butadiene copolymers, butyl rubber, natural rubber and EPDM rubbers. The polymeric materials can contain fillers such as carbon black and fumed silica. Benzofurazan oxide is an example of a source material for the adjacent nitroso groups. The patentees suggest that the furazan oxide can be mixed with the polymeric material using conventional rubber mixing techniques or other conventional plastics or paints technology followed by heating of the mixture to effect modification of the polymer, e.g., cross-linking of the polymer. The common rubber additives may be mixed into the polymer before reacting it with the furazan oxide.
Rubber stocks containing aromatic furazan oxides such as benzofurazan oxide have a sweet odor that can be rather strong and unpleasant. The odor persists even in the vulcanized product. This odor problem can be a severe problem to the use of the furazan oxides in tire stock and treads, not only in the processing of the green stock, but also in the storage of the cured tires. The cause of this strong odor is not known with certainty, but one possible cause may be the conversion of the aromatic furazan oxide to an aromatic furazan.
U.S. Pat. No. 2,974,120 to Miller describes the use of nonaromatic furoxans as antioxidants and antidegradants in rubber. U.S. Pat. No. 2,905,582 to Coleman et al, describes the use of nitroso compounds, including dinitroso compounds wherein the nitroso groups are on nonadjacent carbons in a method for bonding polyurethane resin to rubber bodies. Morita has described the use of N,4-dinitroso-N-methyl aniline as an active chemical promoter for carbon black reinforcement of IIR, NR and SBR. See Rubber Chemistry ,and Technology, Vol. 49, page 1019 and following (1976). Tanaka et al, have reported studies of nitroso benzene in rubber where chain cleavage was observed in Kogyo Kagaku Zasshi 74(8), pages 1701-6 (1971).